Vehicles often include auxiliary equipment that requires power for operation. The auxiliary equipment may be used when the vehicle is stationary and/or moving. For example, a snow removal truck requires operation of a snow plow and/or a salt spreader while the truck is in motion. Snow plows are often controlled by hydraulic systems to raise, lower, and tilt the plow blade. Additionally, a truck that is used to service power and/or telephone lines requires operation of a cherry picker. Cherry pickers are typically controlled by hydraulic systems to raise, lower, and rotate the cherry picker bucket.
In one approach, the hydraulic systems include hydraulic pumps with DC motors that are powered by the vehicle battery. However, such DC motors require a significant amount of power. In another approach, the hydraulic pumps are powered by a power take-off (PTO) system. The PTO system interfaces with an engine shaft of a vehicle to provide rotational power to auxiliary equipment.
Referring now to FIG. 1, an engine shaft 10 of a vehicle 12 is connected between an engine 14 of the vehicle 12 and a torque converter 16. A PTO system 18 includes a PTO gearbox 20 that interfaces with the engine shaft 10 to provide rotational power to an auxiliary device 22. For example, the auxiliary device 22 may include a hydraulic pump. The added load of the PTO system 18 reduces torque that is generated at the engine shaft 10. To provide sufficient torque to support the PTO system 18, an engine control module 24 commands an increase in the speed of the engine 14. For example, the control module 24 may increase the speed of the engine 14 by adjusting throttle position.
The engine 14 includes a throttle position sensor (TPS) 26 and an electronic throttle body (ETB) 28. The TPS 26 generates one or more position signals that indicate a throttle position. The control module 24 adjusts the throttle position by transmitting a throttle adjustment signal to the ETB 28. Since the auxiliary device 22 may not be required to operate continuously, the vehicle 12 includes a PTO control device 30 that communicates with the control module 24.
Referring now to FIG. 2, an exemplary PTO control device 30 includes an on button 38, an off button 40, a speed increase button 42, and a speed decrease button 44. For example, the PTO control device 30 may be mounted inside of the vehicle 12. A user presses the on button 38 when operation of the auxiliary device 22 is required. Pressing the on button 38 may automatically increase the speed of the engine 14 by a predetermined amount. Pressing the on button 38 also enables the speed increase and speed decrease buttons 42 and 44, respectively. A user presses the speed increase button 42 in order to increase the speed of the engine 14. For example, pressing the speed increase button 42 may increase a rotational velocity of the engine shaft 10 by 100 revolutions per minute (rpm). Pressing the speed increase button 42 again may increase the speed of the engine 14 by another 100 rpm. Holding the speed increase button 42 down may continuously increase the speed of the engine 14 by 100 rpm at a predetermined rate. Alternatively, the rate that increments of 100 rpm are added to the speed of the engine 14 may increase while the speed increase button 42 is continuously held down.
The user presses the speed decrease button 44 in order to decrease the speed of the engine 14. For example, pressing the speed decrease button 44 may decrease the speed of the engine 14 by 100 rpm. Pressing the speed decrease button 44 again may decrease the speed of the engine 14 by another 100 rpm. Holding the speed decrease button 44 down may continuously decrease the speed of the engine 14 by 100 rpm at a predetermined rate. Alternatively, the rate that the increments of 100 rpm are subtracted from the speed of the engine 14 may increase while the speed decrease button 44 is continuously held down.
In order to prevent adverse changes in the operation of the vehicle 12, the user is typically unable to decrease the speed of the engine 14 past a default speed of the engine 14 that exists when the user presses the on button 38. However, this assumes that the vehicle 12 is stationary. When the vehicle 12 is moving, the user is typically unable to decrease the speed of the engine 14 past a minimum speed that is sufficient to maintain a current speed of the vehicle 12.
The user presses the off button 40 in order to discontinue operation of the auxiliary device 22. Pressing the off button 40 disables the speed increase and speed decrease buttons 42 and 44, respectively, and returns the speed of the engine 14 to a previous speed of the engine 14 that existed before the user originally pressed the on button 38. For example, if the speed of the engine 14 had been increased by 1000 rpm via the PTO control device 30, the control module 24 decreases the speed of the engine 14 by 1000 rpm when the off button 40 is pushed. In order to prevent abrupt changes in the speed of the engine 14, the control module 24 may ramp any changes in the speed of the engine 14 that are commanded when the off button 40 is pushed.
While the PTO control device 30 allows a user to both increase and decrease the speed of the engine 14, the increments at which the engine speed are increase or decreased are fixed. For example, if the speed increase button 42 increases the speed of the engine 14 by 100 rpm, the user is required to press the speed increase button 42 ten times to increase the speed by 1000 rpm. Additionally, in this case, the user is unable to adjust the speed of the engine 14 in increments that are less than 100 rpm. After a user adjusts the speed of the engine 14 a first time via the PTO control device 30, the user may want to adjust the speed of the engine 14 again. In order to use the default engine speed that existed after the user pressed the on button 38 as a base speed, the user is required to press the off button 40 and then the on button 38 again. This wastes time and puts unnecessary stress on the engine 14 and PTO system 18.